1. Field of the Invention
The present invention relates to a clock signal generation circuit, an optical scanning apparatus, and an image forming apparatus, and more particularly to a signal generation circuit for generating clock signals used when scanning a scanning target with a light beam from a light source, an optical scanning apparatus including the signal generation circuit, and an image forming apparatus including the optical scanning apparatus.
2. Description of the Related Art
In an image forming apparatuses (e.g. laser printers, digital copiers), the light, which is modulated in accordance with image information, is condensed from a light source onto the photoconductor via a polygon mirror, scanning lens, etc., and is moved (scanned) in a predetermined direction (scanning direction), to thereby form latent images (electrostatic images) on the photoconductor. Then, the image information is made visible by attaching toner to the latent images.
In recent years and continuing, the demand for forming images with higher quality is growing. Therefore, under such circumstances, the problem where a beam spot deviates from a predetermined position on a photoconductor cannot be ignored. This problem is caused by, for example, inclination of the deflection/reflection face of the polygon mirror, inconsistency of the distance from the rotation axis of the deflection/reflection face, and changes in the wavelength of the light from the light source.
Various technologies (see, for example, Japanese Laid-Open Patent Application Nos.11-167081, 2001-228415, and 2002-36626) are proposed for correcting the deviation of the beam spot. The aforementioned technologies correct the deviation by correcting clock signals used during the scanning of a photoconductor (hereinafter referred to as “pixel clock signals”). However, with the apparatus disclosed in the aforementioned Japanese Laid-Open Patent Application Nos.11-167081, 2001-228415, and 2002-36626, the signals, which are output from a photo-detecting element serving to detect the timing for starting the scanning of a single line, may be adversely affected by noise. This results in the formation of irregular latent images and leads to the degradation of image quality.